Those challenges include deep rifts in the party over personnel and policies. Mr. Xi’s ascension to president is to be announced at a party congress expected to be held in just weeks. But no date has been set for it, a sign, analysts say, that the party is divided over many critical issues.

The ratcheting up of tensions with Japan is partly a result of this rift. Japan’s actions have played a role in stoking Chinese anger; most recently, the Japanese government bought the islands from their private owner. But some analysts say that the bellicose response by China, including the decision to send six surveillance vessels to the waters around the islands, were intended to increase tensions.

One reason could be a desire to prevent Mr. Xi from taking complete control this autumn. A party scholar with family ties to top leaders, including Mr. Xi, said the departing president, Hu Jintao, is worried that his political base will be weakened under the new leadership team led by Mr. Xi.

[…] But Mr. Xi faces many other challenges. One is how to deal with the disgraced official Bo Xilai, who lost his positions after his wife was accused of murdering a British business associate. Mr. Bo has not been charged with wrongdoing but has disappeared from view, even though he remains popular among many party members. The party also faces economic challenges that will demand painful policy changes.